Angle-stemmed myrtle

Family: Myrtaceae - same family as eucalypts, bottle-brushes and paperbarks.

Conservation status: This species is listed as Endangered in Queensland (Nature Conservation Act 1992) and nationally (Environment Protection and Biodiversity Conservation Act 1999). It is considered a medium priority for conservation under the Department of Environment and Heritage Protection Back on Track species prioritisation framework.

Description

The angle-stemmed myrtle is a tree that grows to a height of about 18 m with a dense canopy of glossy, deep green foliage. The new leaves have a pink flush and the bark is pale brown in colour and is either flaky or scaly. The most distinctive characteristics of this species are the four raised corners on the angled branchlets and the aromatic and pleasant scent of the leaves when crushed. The flowers are white with 4-5 smooth petals, are 6-9 mm in diameter, and occur singly at the base of the leaves. The fruit is a globular, glossy, soft fleshed berry 7-12 mm in diameter that turns black when ripe; it is edible.

Habitat and distribution

The angle-stemmed myrtle is found in lowland riparian rainforest, below the peak flood level, along permanent watercourses subject to tidal influence. The species is currently known from nine sites along the lower reaches of the Brisbane and Logan Rivers and their tributaries, although specimens from the 1800s were also collected from Moggill, southeast Queensland. The current wild population of the angle-stemmed myrtle is 285 individuals. This consists of 73 naturally-occurring mature trees and a further 212 trees that have been planted since 1995.

Life history and ecology

Angle-stemmed myrtle with fruit Photo: Glenn Leiper

The angle-stemmed myrtle reproduces from stem suckers following damage to the main stem or from seed. Buds and flowers appear in late spring (October to November) with the fruits ripening from mid-January to February. The fruits remain viable for only a short period and the quantity and viability of the fruit produced varies markedly from year to year. Flowers of the angle-stemmed myrtle are likely to be pollinated by native bees, although this is yet to be confirmed.

As the seeds are located within a sweet, soft and fleshy fruit, it is suspected that they are dispersed by animals, particularly birds and bats. Other animals such as lizards, small mammals and tortoises may also play a role in seed dispersal. Gravity and water may also play a significant role in dispersal due to the location of trees near waterways even though the fruit does not float.

Seed germination occurs in 8-60 days and nursery-grown seedlings can reach a height of 30 cm in 12 months. It is not known at what age or size the angle-stemmed myrtle reaches maturity.

Threatening processes

The angle-stemmed myrtle is threatened by clearing of habitat, damage by livestock, competition from weeds and the collecting of seeds and cuttings. Impacts from land use in the surrounding areas and human visitation may also be a threat to the long-term survival of the species.

Despite its distribution along waterways, the angle-stemmed myrtle was not impacted by the south-east Queensland flooding in January 2011.

Myrtle rust, a newly introduced disease of plant species in the Myrtaceae Family, may also be a significant threat to the angle-stemmed myrtle. The angle-stemmed myrtle population at Logan has become infected with myrtle rust, but so far the other populations appear to be unaffected. Research is underway by Griffith University to determine the impact of this disease on the angle-stemmed myrtle.

Recovery actions

The angle-stemmed myrtle recovery team has coordinated the propagation and planting of 113 trees at sites where the original plants were found and 99 at new locations. Other recovery actions include weed control, signage, the creation of paths to reduce damage by human visitors, and the fencing of sites to exclude livestock and to restrict vehicle access.

Angle-stemmed myrtles are protected from destruction by tree preservation by-laws of local councils and it is an offence to destroy, remove or collect seeds and cuttings from a protected plant under the Queensland Nature Conservation Act 1992.

The Department of Environment and Heritage Protection is assessing the impact that the south-east Queensland January 2011 flooding has had on the two populations of angle-stemmed myrtle.